1. Field of the Invention
The invention relates to an optoelectric element having a semiconductor body provided on a substrate formed from an electrically insulating material and covered with a luminescent layer for converting electromagnetic radiation of a first wavelength range generated by the semiconductor body into visible light of a different wavelength range.
The invention also relates to a method of covering an optoelectric element with a luminescent layer.
2. Description of the Related Art
A prior art optoelectronic element as just mentioned is disclosed in U.S. Pat. No. 5,813,752. In the known optoelectric element, the semiconductor body and the substrate form part of a LED. The luminescent layer converts UV light or blue light generated by the LED into visible light of a different wavelength range. In this manner, such LEDs can be made suitable for use in different applications requiring visible light of different colors. The problem is, however, that it is often difficult to apply the luminescent layer onto the optoelectric element in such a manner that a closely contacting layer of a readily controlled and substantially uniform thickness is obtained.
Therefore, it is an object of the invention to provide an optoelectric element comprising a closely contacting luminescent layer of uniform thickness, which can be provided in a comparatively simple manner.
To achieve this, an optoelectric element in accordance with the invention further includes an electroconductive layer situated between the substrate and the luminescent layer, the electric conductivity X of which is chosen to be such that, during operation of the optoelectric element, the current through the electroconductive layer is at most 5% of the current through the semiconductor element.
In practice, the electroconductive layer usually connects different electrodes of the optoelectric element to each other. The electric conductivity of this layer is chosen to be so low that the layer does not cause a short-circuit between the electrodes of the optoelectric element, and that the functioning of the optoelectric element is hardly adversely affected. Surprisingly, it has been found that, at the same time, the conductivity is high enough to deposit luminescent material from a suitably chosen slurry by electrophoresis, in which process the electroconductive layer serves as one of the electrodes. In this manner, a closely contacting luminescent layer forming part of the optoelectric element can be readily provided in a uniform thickness, the optoelectric properties of the optoelectric element not being adversely affected by the conductive layer.
It has been found that an optoelectric element in accordance with the invention can be embodied such that, during operation of the optoelectric element, the current through the electroconductive layer is at most 1% of the current through the semiconductor element.
An optoelectric element in accordance with the invention has a comparatively high efficiency if the electroconductive layer is transparent to electromagnetic radiation generated by the semiconductor element.
Favorable results were achieved using embodiments of an optoelectric element in accordance with the invention, wherein the electroconductive layer comprises a transparent oxide, more particularly an oxide selected from the group formed by indium tin oxide, antimony tin oxide and tin oxide, and wherein the semiconductor body forms part of an LED.
The present invention provides a method for covering an optoelectric element comprising a semiconductor body provided on an electrically insulating substrate. The method comprises a step wherein the substrate is covered with an electroconductive layer, after which at least the substrate is brought into contact with a suspension of a luminescent material. The luminescent material is thereafter deposited by electrophoresis on the surface of the electroconductive layer, said electroconductive layer serving as a first electrode, and a second electrode being present in the suspension. A potential difference between the electrodes is maintained, and the electric conductivity X of the electroconductive layer is higher than that of the suspension and lower than that of the semiconductor element.
It has been found that the method can very suitably be used to cover an optoelectric element comprising an LED.
It has also been found that the method in accordance with the invention can be advantageously applied to an optoelectric element connected to a carrier plate on which also a number of optoelectric elements are provided, so that all these optoelectric elements are simultaneously covered with a luminescent layer.